The present invention relates to loading installations for making up nuclear fuel assemblies for inserting fuel rods into a skeleton structure.
Existing assemblies are of structures that are very different from one another. The assemblies used in pressurized water reactors generally comprise a skeleton made up of guide tubes connecting a bottom nozzle to a top nozzle and carrying grids for holding fuel rods in a regular array. Fuel assemblies for boiling water reactors have a variety of structures. Frequently, they comprise a skeleton structure having a central tube interconnecting two nozzles and carrying grids that are mounted to xe2x80x9cfloatxe2x80x9d to a small extent on the central tube in the longitudinal direction. In other cases, the skeleton structure comprises a plurality of longitudinal structural tubes interconnecting two nozzles and each allocated to a substantially square virtual sector occupied by a bundle of fuel rods. Yet other assemblies are of hexagonal section.
Numerous installations are already known for loading nuclear fuel assemblies and that have a skeleton structure defining parallel fuel rod receiving locations arranged in sheets. Such an installation comprises:
a rigid structure for receiving a skeleton structure in a horizontal position;
a magazine for receiving rods to be loaded, placed in a disposition corresponding to the disposition of the rods in the assembly to be loaded; and
a bench for pulling or pushing rods, generally sheet by sheet, from the magazine to the receiving skeleton structure.
An installation of that kind as described in document FR-A-2 709 202 enables rods to be loaded into the skeleton of a fuel assembly for a pressurized water reactor. That installation gives satisfactory results, but it requires major modifications and a considerable down time of the installation when it is desired to switch from loading assemblies of a given type to loading assemblies having rods in a different distribution, for example at a pitch which is different and/or with rods and guide tubes in a different distribution in the array.
The above drawback is shared with all other presently-existing loading installations.
The present invention seeks in particular to provide an installation making it possible to make up successive fuel assembly batches for light water nuclear reactors with short periods of installation down time whenever it is desired to switch from manufacturing one type of assembly to manufacturing some other type, thus providing a high degree of flexibility in use.
To this end, the invention provides an installation for making up a nuclear fuel assembly, the installation comprising:
a rigid structure for receiving a skeleton in a horizontal position;
a magazine for receiving rods for loading in a disposition that corresponds to that of the rods in the assembly; and
a bench for pulling or pushing rods comprising a block of pulling or pushing elements enabling a plurality of rods to be slid simultaneously from the magazine into the inside of the skeleton structure; the installation being characterized in that the pulling bench is designed to receive a block for selecting pull or push elements from a plurality of blocks, each block activating only those pull or push elements that correspond to a particular set of guide plates, and in that the reception structure includes a bench enabling a set of clamps selected from a plurality of sets each corresponding to a particular type of assembly to be secured removably by quick coupling and uncoupling means closed by actuators. The reception magazine generally comprises a housing provided with grooves for receiving any one of a plurality of sets of guide plates, each set corresponding to a particular array that reproduces the array intended for the assembly. Nevertheless, it is also possible to provide a particular type of magazine for each type of assembly.
By replacing only a few components, it is possible to adapt the machine to different rod distribution pitches, to different numbers of rods in an array, and/or to a different distribution of empty locations in an array.
It is becoming more and more commonplace to use fuel assemblies in which at least some of the rods contain not only uranium oxide, but also plutonium oxide and even possibly oxides of other transuranium elements. Such fuel rods have much higher gamma and neutron activity than do new rods containing uranium oxide only.
To reduce the risk of operators being exposed to radiation, the invention optionally proposes an installation in which the reception magazine carried by a support carriage is covered by a biological protection hood of U-shaped cross section bearing against the top face of the carriage. The rigid reception structure of the skeleton structure of the assembly can also be designed to receive a biological protection hood, often implemented in the form of a plurality of parts can be removed separately. As a result, any interventions that turn out to be necessary need only give rise to a small exposure dose.
To further reduce the need for intervention by an operator, the entire operating sequence can be controlled by a central programmed computer and control member capable of having a plurality of programs loaded therein, each corresponding to a different type of assembly. Another solution consists in providing actuators such as electrical or pneumatic actuators that are remotely controlled.
In both cases, the presence of an operator close to the installation is required only for performing the modifications that are necessary for switching from one type of manufacture to another. These operations can be performed when the installation does not contain any nuclear fuel.